1. Field of the Invention
This invention relates to printing and reading of two-dimensional barcode or other form of machine-readable symbology for encoding data, and in particular, it relates to a method and apparatus for enhancing the reliability of reading such barcode.
2. Description of the Related Art
Barcode is a form of machine-readable symbology for encoding data, and has been widely employed in a variety of application fields. Two-dimensional barcode (2d barcode), which is one mode of such symbology, can be used to encode text, numbers, images, and binary data streams in general. One widely used 2d barcode standard is the PDF417 standard, and software and hardware products have been available to print and read such 2d barcode. Color barcode has also been used. 2d barcode is formed of an array of two-dimensional tiles having different values as represented by the printed density and/or color of the tile. The values may be binary (e.g. black and white) or multi-valued (e.g. gray level), and may have a single color channel (i.e. black, red, etc.) or multiple color channels (e.g. red, green and blue). A 2d barcode can be printed on a label and then affixed to an object or a printed document, or it can be directly printed with a document on the same recording medium. A 2d barcode can be read by a specialized barcode scanner, or, if the barcode is a part of a printed document, the document can be scanned and software in the scanner or a computer can detect the barcode and extract the encoded data.